Methods for producing a crystalline polyolefin by polymerizing an alpha-olefin such as propylene or 1-butene in the presence of a stereoregular catalyst have been proposed in many prior art techniques and hence are known. Among these polymerization methods, ones for producing a highly stereoregular polymer with high catalytic activity by polymerizing an alpha-olefin in the presence of a catalyst formed of (a) a highly active titanium solid catalyst component comprising, as essential components, magnesium, titanium, a halogen and an electron donor, (b) an organoaluminum compound catalyst component and (c) an electron donor catalyst component, have been proposed in many prior art documents. These methods are employed on industrial scales as superior polymerization methods that avoid the need for the removal of any catalyst and amorphous polymer from polymers obtained after polymerization based on the methods. However, there is a significant demand for a rationalization technique even in the art, and a technique for polymerization with higher catalytic activity is in need.
Patent Document 1 (JP 2637076 B) discloses a process for producing a propylene block copolymer by the pre-polymerization of propylene in a first polymerization stage using an organoaluminum compound and a solid titanium catalyst component formed by contacting a magnesium compound, a titanium compound and a polycarboxylic acid compound as an electron donor, and the subsequent copolymerization of propylene and another alpha-olefin in a second polymerization stage using the pre-polymerized solid catalyst component, an organoaluminum compound and an organosilicon compound catalyst component as an electron donor. It is disclosed in Example 1 of Patent Document 1 that a solid catalyst component used in the pre-polymerization of propylene in a pre-polymerization step (a first polymerization stage), triethylaluminum (an organoaluminum compound) and n-propyltriethoxysilane (an electron donor) were added to a propylene-purged autoclave to polymerize propylene, followed by the addition of a gaseous mixture of ethylene and propylene into the system to give an ethylene-propylene copolymer. Patent Document 1 discloses nothing about the pre-contact of a pre-polymerized catalyst, an organoaluminum compound and an electron donor before polymerization or the order of the contact of these compounds.
Patent Document 2 (JP 2740503 B) discloses the pre-polymerization of an alpha-olefin using the following components: a titanium solid catalyst component obtained by reacting a magnesium compound with a tetravalent titanium compound and then reacting the reaction product with a polycarboxylic acid ester; an organometallic catalyst component; and an organosilicon compound, and the subsequent alpha-olefin polymerization using the pre-polymerized solid catalyst component. It is disclosed in Example 2 of Patent Document 2 that propylene was pre-polymerized using the following components: a titanium catalyst component comprising titanium, magnesium and diisobutyl phthalate; triethylaluminum; and diphenyldimethoxysilane, followed by the addition of the resulting pre-polymerized catalyst, triethylaluminum and diphenyldimethoxysilane to a propylene-containing autoclave to polymerize propylene. Patent Document 2 discloses nothing about the pre-contact of a pre-polymerized catalyst, an organoaluminum compound and an electron donor before polymerization or the order of the contact of these compounds.
Patent Document 3 (JP 3984304 B) discloses that polypropylene is produced using an olefin polymerization catalyst formed of: a contact product prepared by contacting a solid titanium catalyst component comprising magnesium, titanium, a halogen and an electron donor, an organometallic compound catalyst component and an organosilicon compound; a 1,3-diether compound; and an organometallic compound catalyst component. It is disclosed in Example 1 of Patent Document 3 that propylene was pre-polymerized using a solid catalyst component formed of magnesium chloride, titanium tetrachloride and diisobutyl phthalate; triethylaluminum; and dicyclopentyldimethoxysilane, followed by the charging of the resulting pre-polymerized catalyst, triethylaluminum and 2-isopentyl-2-isopropyl-1,3-dimethoxypropane into an autoclave charged with propylene to polymerize propylene. Patent Document 3 discloses nothing about the pre-contact of a pre-polymerized catalyst, an organoaluminum compound and an electron donor before polymerization or the order of the contact of these compounds.
Patent Document 4 (JP H07-23406 B) discloses a method by which propylene is pre-polymerized using a titanium complex comprising a magnesium halide and a titanium halide and an organoaluminum compound and then a propylene polymer is produced using the resulting solid catalyst component, an organoaluminum compound catalyst component and an organosilicon compound. It is disclosed in Example 1 of Patent Document 4 that a pre-polymerized catalyst, t-butylmethyldimethoxysilane and triethylaluminum were added to an autoclave to polymerize propylene. Patent Document 4 discloses nothing about the pre-contact of a pre-polymerized catalyst, an organoaluminum compound and an electron donor before polymerization or the order of the contact of these compounds.
As described above, it is widely known to pre-polymerize propylene before using a solid titanium catalyst component comprising magnesium, titanium, a halogen and an electron donor compound. However, there is no prior art document that discusses either the pre-contact of a pre-polymerized catalyst, an organoaluminum compound and an electron donor compound with each other before using the pre-polymerized catalyst in a main polymerization, or the order of the contact of those compounds.